AFAIK water volume differs by +-5% (somewhere there) between 35*F and 212*F. I was thinking of increasing the volume indicators on my BK to compensate.
(This could be a reason for "low efficiency" in some breweries as volume is determined at room temperature and results in a 1/2 gallon "loss" in a 10 gallon batch when the wort cools.)
In other words measure volume of HLT and MLT at room temp or colder and volume of BK adjusted by 5%.

It'd be difficult for you to account for unless you're always adding the same temperature water. It's about a 4% change from 70F to boiling, but only 2% if you're adding 150 degree wort from your mash tun.